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  1. #1
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    Default Tips for priming a 12V71

    Ran the tank dry on our new to us 12v71 yesterday. Any good tips for priming the fuel system? Doesn't appear to be a manual lift pump like other engines usually have

  2. #2
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    Default Re: Tips for priming a 12V71

    The more fuel you can get in the tank prior to your starting attempts....the better. The fuel pump for the Detroit is a self priming, positive displacement pump. But...it sometimes needs a bit of help.

    Make sure that your tanks are truly running "dry" and that the problem isn't really with a broken or cracked pickup tube. You would want to rectify that issue right away before putting to sea.

    There SHOULD be at least one CHECK VALVE protecting the fuel from draining back to the tank(s) installed somewhere NEAR or ON the first filter or water separator. Make sure that is in place and FUNCTIONAL. If the engine has been starting reliably up to now...then all is probably ok there. BUT...you will want to KNOW where all this is in the event you have any problems on the water.

    Start with AT LEAST 15-20 gallons of fuel in the tank.

    Anywhere that there can be a "void" between the end of the pickup tube in the tank and the pump....as in the RACOR water separator OR the PRIMARY fuel filter(s)....OR BOTH....fill those spaces with fuel. This is where you would have an opportunity to replace the fuel filters.

    Also....any air pocket that may exist between the pump and the FUEL INJECTORS....IE: The SECONDARY fuel filter(s)...will temporarily starve the injectors for fuel and the engine may balk at firing. Fill that space with fuel as well. You also DO NOT want the injectors being "plunged" (depressed by the rocker arm) with no fuel in them. They are lubricated with the fuel and that might cause damage. Here again, you could use this opportunity to replace the filter(s)

    Sometimes....after doing all of this....engines that have been run dry will not want to start. This is usually because the fuel tank is either very remote or much lower than the engine....or both. What will happen is that there will be air pockets in the suction line and after an unsuccessful attempt at starting you will find that...
    .... "HEY"! "the primary filter is low on fuel again"! "I know I just filled it up"!
    A small air pocket can make a BIG difference. So, in many cases, a guy may find himself having to fill the filter cavities SEVERAL times to get the engine to fire. This is a VERY FRUSTRATING occurrence.

    But, if you can get the engine to fire and REV it hard right at the beginning...the pump will turn MUCH faster and overcome these pockets on the FIRST TRY.

    So.....I will give you my $110,000 secret method for getting her going on the second attempt should the first attempt fail.

    I carry a 1 ft. long section of 1/4" braided fuel line in my "road bag". On one end of the fuel line is one of those FUEL CHECK VALVES I mentioned earlier. This little "trick" will work without it BUT....when the engine fires...you WILL get SOAKED in diesel fuel!

    The SECONDARY fuel filter adapters always have 1/4" or 3/8" pipe thread plugs in them for configuring for different mounting circumstances. These plugs are also a great access point for taking fuel pressure readings. So you may find a pressure sender or a mechanical gauge threaded in these access points too.

    I use this point to fit my little "blow pipe" to the filter adapter. When you've topped all off and are ready to fire the engine....blow hard into the fuel line (yes, with your mouth) while someone else cranks the engine and works the throttle. You don't have to blow hard as in PASSING OUT hard...just give it good POOF!

    AS SOON AS THE ENGINE FIRES, GO TO FULL THROTTLE and run it at full no load for AT LEAST 30 seconds. This ensures that ALL the voids are clear and there will be no more issues with starting when you're finished.

    If you didn't use the check valve in the blow pipe (arrow points to the engine...away from YOU)...You will be completely SOAKED in fuel. However...if you followed the instructions....the engine will be HOWLING at full song...you will be DRY..... and you can now idle her down...shut her off ....and QUICKLY remove the blow pipe and QUICKLY replace the pipe plug.

    DONE!

    Good luck with your "new" Detroit.

  3. #3
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    Default Re: Tips for priming a 12V71

    Thanks for that. Boat is new to us and the fuel tank is low but not completely empty when I dipped it. Unsure however how close the pickups get to the tank bottom though. The pickup for the genset from the same tank also appears to sucking air so pretty hopeful that it is just a shortage of fuel. I also found some air in one of the v12's twin primary filters so I am guessing that this is the issue. Talked to an old school mechanic friend and e suggested using a vacuum pump to pull fuel through to the secondary filter and get all the air out once we refill the tank. Will give that a try and then if it doesn't work will setup your patented starting technique a try. Boat ran out of fuel at the dock so fortunately no big deal. Do need to sort out the fuel gauge though as wouldn't want this to happen at sea. This particular engine is supposedly an original new crate long block that has been in storage for a couple of decades. It was in the boat when we bought it so can't be 100% sure, but everything we have found out since seems to support this being the case. Had zero gauges etc when we got the boat and start/stop was done mechanically in the engine room. Got everything up to the wheelhouse now along with fitting the GPS, Radar etc so starting to look a bit more normal. Biggest issue there now is that I need to find a commercial quality compass for a steel boat without spending more than we paid for the boat.

  4. #4
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    Default Re: Tips for priming a 12V71

    The people that do steel boats and compasses better than anyone else is the good ol' UNITED STATES NAVY. I'm near San Diego so that's what I would do....start looking for some surplus equipment rather than brand new store bought.

    N.E.W. = Never Ever Worked.

    Yes! I will be interested to see how you make out with the vacuum approach. I never tried that because I was taught "my" method many, many moons ago and it's quick, dirty and effective with no moving parts and no electricity required.

    One thing that makes me think you MIGHT have difficulty with, using that method, is that the return line goes back to a higher fitting in the tank and you will undoubtedly be pulling on that line as well as the supply side. So...physics being what they are...the "path of least resistance" comes into play. It makes me wonder if your vac pump will just pull in air from the tank.

    But, with the RESTRICTED FITTING in there to slow things down....I don't know. Only ONE way to find out!

    AND if you are intending to, indeed, refill the tank before the attempt....that will help immensely.

    As far as the pickup tubes go...it is usual to find that the tank will be constructed with a small "pan" area that presents a low spot for the pickup to pull from. This is not always the case though and, even with that, you might suck air because of a wake going through the docks and causing the fuel to slosh a bit. It only take a second to pull in an air pocket. So, finding the fuel level as low as you did probably indicates she just sucked in some air. But, do take note of that level you have in there now and you will know just how low you can go. Wouldn't want that to happen again coming in to a marina or off the bow of a container vessel!

    The injectors are lubed and cooled...somewhat....with the fuel too so keeping it as high in the tank as is feasible is always a good practice.

    That 12v71 is one ROCK SOLID engine! That engine has probably moved MORE DIRT in this country than any other. CATERPILLAR is likely STILL trying to catch up with the yardage of the old TEREX earth movers with the 12v71 in the front and 6v71 pushing in the back. And they haven't made any of that stuff in DECADES! If she starts (with fuel of course) easily and idles with little to no smoke....your crate engine story may very well be true. And, if so, you should get a WHOLE bunch (thousands of hours) of trouble free service.

    Let us know how it goes with the restart.

  5. #5
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    Default Re: Tips for priming a 12V71

    Well I replaced lips & valve with an electric priming pump running from a can of clean fuel connected to the engine mounted filter. Managed to get fuel right through to the tank return so figured that would be good. Still no run though. Funny thing is that every time I try to start I get pressured air when I crack one of the lines from the filter to the head rails. Now looking at whether I might have an air leak somewhere on the fuel filter/lines/tank side. Have checked everything once with no obvious result, so will now go through it more methodically. Had something similar a few years back where the internal tank pickup had developed a pin hole. Will start with a proper tank/feed inspection I think. Fortunately this tank ~550gal can be completely opened up by removing the top. Unfortunately that involves maybe 100+ large bolts being undone and they might not have been moved for 40 years. Will keep you updated.

  6. #6
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    Default Re: Tips for priming a 12V71

    Yep...she is sucking air in someplace before the pump. Was anything opned up? Like Racors or primary filter? If the bowl on Racor didn't seat or if a gasket on a spin in filter got "bunched up" that could cause this. Keep looking...you'll find it.

    I would NOT want to be the one to snap off the head to one...or 5...or 8 of those tank cover bolts! Well, on second thought, I wouldn't so much mind being the one to snap them off....but I wouldn't want to be the guy that had to drill and snag 'em with an EZ out! :+)

  7. #7
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    Default Re: Tips for priming a 12V71

    Just realised I forgot to update this thread after the fix. I used the small electric pump off the 2 cyl Lister genset to run fuel pressure into the 12V71 fuel pump. Wound it over a bit with the fuel lines cracked open at various places until I was getting air free fuel everywhere. Engine would then kick when you first stated to wind it over, but not start. Very strange for an engine that starts on the first revolution every time. At that stage I figured I had fuel and compression, so probably not enough air. I am still learning this engine, but remembered that they might have an emergency air shut off for stopping a runaway condition. Popped the intake plumbing off the top of the superchargers and sure enough there was the closed flap. Pushed it back into open position and checked out the little cam mechanism arrangement for future reference. It is hidden in an awkward to get at spot on this installation, but I will rig up a solenoid and switch to make it operational again. engine started first turn after that and is running great again. Only thing I have noticed since is that I am getting a small oil leak out of a small hole in the exhaust on one side. Not sure what this might mean?

  8. #8
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    Default Re: Tips for priming a 12V71

    Yep, you're learning your way around the old girl. If you have the newer style, spring loaded injector rack tubes, the chances of a runaway are slight. But, if it has the old style tubes with each injector rack arm rigidly attached to the tube, just one injector sticking in full fuel position would be a reason rigging up that E-Stop, so that it can be quickly deployed, is imperative.

    The oil leak:
    Is it actually coming from the exhaust? The reason I ask is that all Detroit 2 strokes are DESIGNED to leak from the drains in the blower box. On many boats the drains are routed to various devices to catch the oil. Some of these capture the oil and hold it for regular draining. This regular drip drip drip MUST take place to prevent the air box from slowly filling with oil and swamping the cylinder liner intake ports.

    If the oil is truly coming from the exhaust, it may not be unusual for an engine that has been sitting to pass a bit of oil on startup as the rings set in again.

    If the engine has exhaust valve guide seals installed they may have hardened up from sitting and may need replacing. But, you can run the old girl for a bit and see if the hot oil softens them up and gets them to sealing again. It's a real pain replacing valve stem seals on an engine with 48 exhaust valves!

  9. #9
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    Default Re: Tips for priming a 12V71

    Thanks JG. Any easy way to check which racks we have? Will follow up the oil leak when we put her back in the water. I need to identify the blower box drains as well to see how they are plumbed on this one. Where do I find those typically as well please?

  10. #10
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    Default Re: Tips for priming a 12V71

    The rack arm ID is easy. With the governor in no fuel position, pop a valve cover and look at an arm where it attaches to the control tube. There might be a coil spring there. Take your index finger and push on the end of the arm where it is connected to the injector rack and push inward. On spring equipped rack tubes, each injector rack will push in and spring back to no fuel position when released. On the older tubes without springs, the injector rack will not move unless they ALL move.

    This is why only one injector hung in full fuel can hold all the injectors in ful fuel and over speed the engine on a non spring rack tube.

  11. #11
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    Default Re: Tips for priming a 12V71

    The blower box drains are typically 1/8" npt holes on each side of the engine block approximately 3" above the oil pan flange. They could have some sort of pipe fitted screwed into them and possibly have flared steel tubing extensions to direct the air and oil into a container.

    Engines equipped with AIR-SEP systems often have the drains going into the crankcase oil recovery portion of the AIR-SEP.

    Whichever way the drains are plumbed, you must know that they need to be kept clear and flowimg air so that the air box never fills with oil. A steady drip of oil at idle is normal for these engines.

  12. #12
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    Default Re: Tips for priming a 12V71

    I've been running Detroit Diesels since they were Gray Marine. The only time I have had a no fuel issue or air in fuel issue was because of a hole or bad fitting in the fuel line. Any DD I have run in the last 30 years, I have a electric pump in the fuel line that is normally off, but used when the secondary filter is changed. It also doubles as an emergency pump inf the regular pump fails (never happened to me).
    Check your fuel lines, any place they might rub for a hole.
    Other than a mechanical failure, the cause for a Detroit not starting is no fuel, air in the lines and not reaching ignition temperature. If the cylinder liners, rings are worn, enough air may escape so the compression doesn't heat the air above ignition temperature. If it has a block heater, turn it on for a couple hours.

  13. #13

    Default Re: Tips for priming a 12V71

    I had to look up Gray Marine that Lepke mentioned above as I had not heard of it. Gray Marine made the engines, from GM diesel division blocks that powered the Higgins boats that were used for the D-Day invasion- helping to save the somewhat free world we know today!



    https://en.wikipedia.org/wiki/Gray_M..._Diesel_Engine


    https://en.wikipedia.org/wiki/LCVP_(United_States)


    https://en.wikipedia.org/wiki/LCVP_(...WII_museum.jpg


  14. #14
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    Default Re: Tips for priming a 12V71

    A really nice feature of the 71 series engines, everything, engine, pumps, blower, etc., is designed to be rebuilt in the field. Sherman tanks that the marines used had 671s. Also they powered generators and so on. Many ships built in WWII had 71 series driven generators.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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